Method of coating paper products with cellulose-wax compositions



United States Patent 3,332,798 METHOD OF COATING PAPER PRODUCTS WITH CELLULOSE-WAX COMPOSITIONS George J, Kautsky, El Cerrito, Calif., assiguor to Chevron Research Company, a corporation of Delaware 'No'Drawing. Filed Jan. 3,1963,'Ser. No."249,140 Claims. (Cl. 117-157) This invention is directed to a method of coating paper products with improved wax compositions whichwill withstand severe abuses to which wax coated containers are sfis eaeaf For many years, paraflin waxhas been used as coatings for numerous laminated materials, including its use as a coating'material forpaper sheetings of moisture proof packages and wrappers, particularly as a coating for the paper used for paper milk cartons. In order to be satis- 3,332,798 Patented July 25, 1967 ice - tanoate, cellulose trioctanoate, cellulose tn'decanoate, celfactory for such use, wax coating compositions should have not only high gloss, low tackiness, and resistance to the transmission of water vapor, but wax coating compostions should also be resistant to scufiing and flaking.

For the most part, wax compositions have low resistance to scuffing; a tendency to crack and peel from containers; and a strong tendency to block; that is, for layers of Waxed papers to adhere together.

Wax compositions often flake off from milk cartons during rough handling and the flaked wax slufis into the milk. Also, wax compositions rupture when the packaging material is creased, permitting water vapor transmission through the ruptured creased package, and furthermore, wax films rub off from containers onto packaging machinery and clothing, leaving a soiled appearance where such a rub-01f occurs.

It is necessary therefore to improve such characteristics of wax coatings sufficiently so as to improve the resistance to tear and erosion of the coated paper. Polyethyl ene has been added to wax blends for the purpose of imparting improved tensile strength to the resulting wax composition. However, the problem associated with the preparation of paraflin wax compositions resistant to scuffing, 'etc., is not solved by simply improving the tensile strength of the wax composition. Polyethylene-wax films on containers are easily marred by scuffing, resulting in the loss of the glossy and pleasing appearance of the container to which such a composition'has been applied.

It is a primary object of this invention to set forth a methodofcoating'of paper products by wax compositions which are resistant to 'scufiing and flake-off, have increased toughness and flexibility, andwhich have increased anti-blocking characteristics.

In accordance with this invention, it has been discovered that fracture-resistant wax compositions are obtained by incorporating cellulose esters or cellulose ethers in paraffin wax compositions. Thus, the wax compositions of this invention consist of paraffin wax'and cellulose esters or paraffin wax and cellulose ethers. j

The coating of paper products by the wax compositions of this invention permits the formation of wax-coated milk cartons and other containers, which will resist wax flake-01f on rough handling, will retainhigh gloss char acteristics, and which .will resist rubbing off onto packaging machinery and clothing. I

The certain particular cellulose esters which are used herein to'improve wax compositions are the alkyl esters of cellulose wherein the celluloes molecule contains, on the average, 3 alkyl radicals per glucose unit; that is these cellulose esters are the tri-esters of cellulose.

Examples of cellulose esters are those wherein the ester groups are identified by alkyl radicals each containing from 7 to 16 carbon atoms, which include cellulose triheplulose trilaurate, etc.

The cellulose ethers include the diand tri-ethers of cellulose wherein the ether radicals are hydrocarbon radicals, preferably alkyl radicals each having from 1 to 18 carbon atoms, with the combined total number of carbon atoms being at least 12; that is, although each of the hydrocarbon ether radicals on each glucose unit of the cellulose has from 1 to 18 carbon atoms, the total number of carbon atoms in the ether radicals on each glucose unit must be at least 12. In the case of diethers, one of the ether radicals must contain at least 8 carbon atoms.

The ethers of cellulose are exemplified as follows: cellulose; methyl octyl ether, cellulose ethyl octyl ether, cellulose ethyl decyl ether, cellulose ethyl dodecyl ether, cel lulose: ethyl 'tetradecyl ether, cellulose propyl octyl ether, cellulose butyl octadecyl ether, cellulose methyl butyl amyl jether, cellulose tri(butyl) ether, cellulose methyl octyl octadecyl ether, etc.

Although only the di-ethers of cellulose are specifically noted as the wax additives in the data hereinbelow, it is understood that a minor amount of the triethers was also present in the wax compositions.

The cellulose itself prior to the etherification or esterification has a molecular weight ranging from 40,000 to 500,000.

The paraflin waxes (e.g., petroleum parafiin waxes) which are improved by the addition thereto of cellulose esters or cellulose ethers include parafiin waxes (and blends thereof) having average melting points in the range of 125 F. AMPto 165 F. AMP, preferablyfrom 125 F. AMP to 156 F. AMP. (The term AMP refers to American Melting Point, as defined inASTM D87-42.)

The cellulose esters and the cellulose ethers are used in the wax compositions in amounts of 2% to 30% by weight, preferably, 10% to 20%, by weight.

Although not necessary, it is beneficial to incorporate a plasticizing agent in the final wax composition. In numerous instances, this plasticizing agent, which can be used in minor amounts such as from 0.5% to 10.0% by Weight, makes it possible to use beneficially larger amounts and larger variety of cellulose esters or cellulose ethers.

Beneficial plasticizers are those having an oil-solubilizing hydrocarbon radical having from 18 to 30 carbon atoms at one end of the molecule and a neutral. polar group at the other end of the molecule. The polar groups include ester radicals .having from 1 to 18 carbon atoms,

' stearate; mixed hexyl and decyl methacrylate polymers,

hexadecanoic acid amide, octadecanoic acid amide, N- methyl octadecanoic acid amide, N,N-di butyl-octadeca noic acid amide, N,N-butyl-octyl octadecanoic acid amide, etc.

The test data presented in Table I hereinbelow show the effectiveness of the cellulose derivatives in improving the desirable characteristics of paraffin wax compositions. .The modulus of rupture was obtainedby pouring a sample of molten wax into a pan of hot water to give a wax slab 0.15 inch thick. Specimens 0.5 inch by 3 inches were cut from this slab and placed on supports 2 inches apart in a modulus of rupture testing device. A force was applied to the center of the test specimen at the rate of 18 ounces per minute. The mass in grams required to break the specimen was recorded. The modulus of rupture was then calculated by the formula:

MR: (Bow) 3 wherein A=mass in grams required to break specimen, B=thickness of specimen in inches, and C=width of specimen in inches N=Oxazoline wax O=Polyglycol PG 2000 P=Pentaerytritol stearate R=Hexyl, decyl methacrylate polymer TABLE I Composition Test Data Paraflin Wax Cellulose Plastlcizer Derivative Mod Flexibility, Rupture 10- inch Type Wt. Type Wt. Type Wt.

percent percent percent 1 A 100 480 23 2 A 70 F 30 1, 200 250 3. B 100 740 18 4 B 70 F 30 1,000 340 5. A 93 C 2 N 5 Improved 6. A 78 D 20 M 2 900 400 7. A 75 E 20 M 5 900 350 8 A 88 F M 2 590 200 9 A 83 F M 2 750 380 10 A 78 F M 2 950 430 11 A. 78 G 20 M 2 750 300 12--...- A 75 F 20 O 5 1,000 350 13-....- A 75 F 20 L 5 1,200 200 14 A 70 F 20 N 10 1, 200 450 15. A 78 I 20 M 2 900 250 16 A 78 J 20 M 2 700 250 17..-" A 70 F 20 O 10 850 320 18 A 75 F 20 L 5 829 300 19 A 75 F 20 P 5 800 510 20..-" B 78 D 20 M 2 1,000 450 21..." B 78 F 20 M 2 1,100 450 22..- B 68 F M 2 1, 000 440 23 B 75 F 20 R 15 1,100 1,200

The flexibility was determined according to the method proposed for testing the breaking strength of petroleum waxes. By means of this proposed method, which is fully described in Appendix VI of ASTM Standards on Petroleum Products-1958, pages 10984100, it was possible to measure the vertical distance in inches the wax specimen bent before breaking into two parts at 40 F.

In modifications of this method as used herein, instead of using a water-loading method for applying a pulling force, an Instron machine was used to apply the force.

The cross-head speed was 0.5 inch per minute.

In the data hereinbel-ow, the base wax A was a parafiin wax having a melting point range of 125-130 F. AMP.

Base wax B was a parafiin wax having a melting point range of 154 F. to 156 F. AMP.

The cellulose derivatives which were used are identified as follows:

C=Cellulose trivalerate D=Cellul0se triheptanoate E=Cellulose trioctanoate F=Celulose tridecanoate G=Cellulose trilaurate H=Cellulose ethyl, octyl ether L=A mixture of primary amides consisting of 25% hexade-canoic amide, octadecanoic amide and 5% octadecanoic amide I claim:

1. A method of coating paper products to provide fracture resistant coatings which have increased toughness, which comprises coating onto a paper base a composition comprising parafiin wax having average melting points in the range of to F. AMP and from 2% to 30% by weight of esterified cellulose having an average of 3 aliphatic ester groups per glucose unit, said esters having alkyl groups of from 7 to 16 carbon atoms.

2. A method according to claim 1, wherein the cellulose prior to esterification has a molecular weight in the range of 40,000 to 500,000.

3. A method according to claim 2, wherein from 0.5 to 10% by weight of a plasticizer having an oil solubilizing hydrocarbon radical of from 18 to 30 carbon atoms is present.

4. A method according to claim 2, wherein from 0.5 to 10% by weight of a mixed hexyl and decyl methacrylate polymer is present as a plasticizer.

5. A method according to claim 2, wherein the acid portion of said cellulose ester is of 10 carbon atoms.

References Cited UNITED STATES PATENTS 2,044,804 1/ 1936 McNally et al. 106-191 XR 2,102,207 12/ 1937 Hunt et al. 3,140,268 7/1964 Halpern et al. 260-285 X 3,183,197 5/1965 Richardson et al. 106--191XR FOREIGN PATENTS 325,014 2/ 1930 Great Britain.

326,482 3/1930 Great Britain.

143,297 1/1931 Switzerland.

ALEXANDER H. BRODMERKEL, Primary Examiner, I. H. WOO, Assistant Examiner, 

1. A METHOD OF COATING PAPER PRODUCTS TO PROVIDE FRACTURE RESISTANT COATINGS WHICH HAVE INCREASED TOUGHNESS, WHICH COMPRISES COATING ONTO A PAPER BASE A COMPOSITION COMPRISING PARAFFIN WAX HAVING AVERAGE MELTING POINTS IN THE RANGE OF 125* TO 165*F. AMP AND FROM 2% TO 30% BY WEIGHT OF ESTERIFIED CELLULOSE HAVING AN AVERAGE OF 3 ALIPHATIC ESTER GROUPS PER GLUCOSE UNIT, AND ESTERS HAVING ALKYL GROUP OF FROM 7 TO 16 CARBON ATOMS. 